Soaking up the sun and boosting vitamin D through diet or supplements may both play a role in preventing multiple sclerosis, Australian researchers found.

In a case-control study, more time spent in the sun — beginning in childhood — independently predicted lower risk of having a first demyelinating event with 30% lower adjusted odds for each 1,000 kJ/m2 of vitamin D-producing ultraviolet rays, according to Robyn M. Lucas, PhD, of the Australian National University in Canberra, and colleagues.

Serum vitamin D levels also independently predicted MS incidence with 7% lower risk of a first event per 10 nmol/L higher 25-hydroxyvitamin D (95% confidence interval 0.86 to 1.00), the group reported in the Feb. 8 issue of Neurology.

When sun exposure measures and serum vitamin D were included in the same model, both came out independently associated with MS risk.

These findings strengthen the link seen in prior epidemiologic studies of the autoimmune neurologic disorder, the researchers noted.

Some other types of autoimmune disorders have been linked to vitamin D deficiency as well, noted internist Len Horovitz, MD, of Lenox Hill Hospital in New York City.

“Vitamin D has a role in prostate health, colon health, breast health, and immune system function, including wound healing,” he said in a statement sent to reporters.

But insufficient levels are common due to lack of sun exposure, Horovitz explained, pointing out that food sources alone can’t provide all the vitamin D the body needs.

Vitamin D supplementation has been increasingly recommended for MS patients, not only for bone health but also in hopes of immunomodulation.

If the case-control study findings mark a true causal impact on MS risk, that strategy alone may not cut it, Lucas’ group noted.

Since sun exposure had an additive, independent effect on risk, “advocating vitamin D supplementation alone may be a less effective preventive intervention than has been suggested by previous epidemiologic studies,” they wrote in their Neurology paper.

The group examined results from the multicenter Ausimmune case-control study of individuals living in four regions of Australia spread across latitudes from 27° S (the same degree south of the equator that a parallel line through Texas and Florida is north of the equator) to 43° S (the Southern Hemisphere equivalent of the line that runs through Oregon and Wyoming in the Northern Hemisphere).

The analysis included 216 individuals ages 18 to 59 diagnosed with MS from November 2003 through December 2006. Another 395 individuals without MS served as controls, matched for age, sex, and study region.

More time spent in the sun, both recently — in the prior three years — and cumulatively during leisure time since age 6, was associated with lower risk of a first MS event (adjusted odds ratio 0.85, 95% CI 0.72 to 1.00, and 0.70, 95% CI 0.53 to 0.94).

The association didn’t change with further adjustment for use of sun protection, the researchers noted.

These self-reported measures were reinforced by a similar link between greater actinic skin damage caused by sun exposure and lower risk of MS incidence (adjusted P=0.006 for trend).

The connection between serum vitamin D and MS showed no threshold for effect and remained unaltered by further adjustments for phenotypic factors like eye color or shade of skin.

Time from MS onset to examination in the study — potentially allowing for confounding by individuals starting vitamin D supplements after diagnosis — didn’t appear to account for the results as serum vitamin D levels and association with first MS events weren’t influenced by time lag, the researchers noted.

Together, the vitamin D level and sun exposure measures appeared to account for 32.4% of the difference in incidence of MS at higher versus lower latitudes in Australia.

The researchers cautioned that vitamin D status was based on a single measurement in the study, which may not have reflected long-term levels, and that self-reporting of sun exposure may not always have been accurate.

1. From the National Centre for Epidemiology and Population Health (R.M.L., K.D., A.J.M.), The Australian National University, Canberra; Murdoch Childrens Research Institute (A.-L.P., T.D.), Melbourne; Queensland Institute of Medical Research (P.C.V.), Brisbane; The University of Queensland and Royal Brisbane and Women’s Hospital (M.P.P., A.C.), Brisbane; Menzies Research Institute (B.V.T., I.v.d.M.), Hobart; Centre for Neuroscience (T.J.K.), The University of Melbourne, Melbourne; Department of Neurology (C.C.), Barwon Health, Geelong; and Department of Neurophysiology (D.W.), John Hunter Hospital, Newcastle, Australia.

1. Address correspondence and reprint requests to Dr. Robyn Lucas, National Centre for Epidemiology and Population Health, The Australian National University, Canberra 0200, Australia Robyn.Lucas@anu.edu.au

Abstract

Objectives: To examine whether past and recent sun exposure and vitamin D status (serum 25-hydroxyvitamin D [25(OH)D] levels) are associated with risk of first demyelinating events (FDEs) and to evaluate the contribution of these factors to the latitudinal gradient in FDE incidence in Australia.

Methods: This was a multicenter incident case-control study. Cases (n = 216) were aged 18–59 years with a FDE and resident within one of 4 Australian centers (from latitudes 27°S to 43°S), from November 1, 2003, to December 31, 2006. Controls (n = 395) were matched to cases on age, sex, and study region, without CNS demyelination. Exposures measured included self-reported sun exposure by life stage, objective measures of skin phenotype and actinic damage, and vitamin D status.

Conclusions: Sun exposure and vitamin D status may have independent roles in the risk of CNS demyelination. Both will need to be evaluated in clinical trials for multiple sclerosis prevention.

Footnotes

Study funding: Supported by the National Multiple Sclerosis Society of the United States of America, the National Health and Medical Research Council of Australia, the ANZ William Buckland Foundation, and Multiple Sclerosis Research Australia.